[Mitochondrial DNA mutations in the pathogenesis in the head and neck squamous cell carcinoma]

Molecular alterations of mitochondrial D-loop in oral leukoplakia

BACKGROUND

Over the years, numerous studies proposed a crucial role of mutations of nuclear DNA in the carcinogenesis process. Of late, many researchers suppose that alterations of mitochondrial DNA should not be excepted from this analysis. Mutational analysis of mitochondrial DNA displayed that mitochondrial D-loop is assessed as a hotspot for molecular alterations in various types of malignant tumors encompassing oral squamous cell carcinoma. Squamous cell carcinoma is believed to emerge through precancerous stages, which might be merely morphologic aspects of cumulative genetic variations.

METHODS

In keeping with this model of molecular tumor progression, this study aimed to investigate the qualitative and quantitative alterations that might occur in mitochondrial D-loop in oral leukoplakia whether dysplastic or not by semiquantitation of a product of the polymerase chain reaction and sequence analyses of mitochondrial D-loop gene.

RESULTS

Statistically significant increases in the mean values of D-loop concentrations were observed across the dysplasia gradient of oral leukoplakia. Sequence analyses revealed the presence of point mutations in both dysplastic and nondysplastic oral leukoplakia but not in normal mucosa.

CONCLUSION

The results of this study suggested that quantitative and qualitative alterations in mitochondrial D-loop could be a promising molecular marker for early detection and progression of the malignancy.

Do CO2 and oxidative stress induce cancer?: a brief study about the evaluation of PON 1, CAT, CA and XO enzyme levels on head and neck cancer patients

Head and neck cancer (HNC) is one of the most common malignancies in the world. HNC is a group of cancers that starts in the mouth, nose, throat, larynx, sinuses, or salivary glands. According to this section of the body parts; induction of cancer can be associated with CO₂ and oxidative stress. The aim of this study is to assess the activities of carbonic anhydrase (CA), catalase (CAT), paraoxonase1 (PON1), and xanthine oxidase (XO) activities in 89 HNC patients and 115 healthy volunteers. Paraoxonase1 activity was found lower in HNC cancer patients. There is no statistically significant difference between patients and controls for catalase, carbonic anhydrase, and xanthine oxidase enzyme levels. According to this results, paraoxonase1 levels could be a candidate as an oxidative marker in HNC patients, but further studies are needed to investigate the other type of cancer related PON1 and the other enzyme levels.

Association between mitochondrial DNA variations and schizophrenia in the northern Chinese Han population

To determine whether mitochondrial DNA (mtDNA) variations are associated with schizophrenia, 313 patients with schizophrenia and 326 unaffected participants of the northern Chinese Han population were included in a prospective study. Single-nucleotide polymorphisms (SNPs) including C5178A, A10398G, G13708A, and C13928G were analyzed by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP). Hypervariable regions I and II (HVSI and HVSII) were analyzed by sequencing. The results showed that the 4 SNPs and 11 haplotypes, composed of the 4 SNPs, did not differ significantly between patient and control groups. No significant association between haplogroups and the risk of schizophrenia was ascertained after Bonferroni correction. Drawing a conclusion, there was no evidence of an association between mtDNA (the 4 SNPs and the control region) and schizophrenia in the northern Chinese Han population.

DNA damage and oxidant-antioxidant status in blood of patients with head and neck cancer

Oxidative stress induces a cellular redox imbalance that has been found to be present in various cancer cells, and overproduction of free radicals may be related to oncogenic stimulation. We investigated the activity of the following antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and malondialdehyde (MDA) concentrations in blood of patients with head and neck squamous cell carcinoma (HNSCC) compared with the control group. A comet assay was used to assess DNA damage. A nonsignificant increase of MDA and a decrease of SOD, CAT, and GPx (p>0.05) were seen in HNSCC patients compared with controls. It was found that the level of oxidative DNA damage in HNSCC patients was significantly higher compared with the control group (p ≤ 0.001). Our observations suggest that HNSSC patients may represent an impaired antioxidant defense system, resulting in DNA damage and genome instability. It has to be also considered that an oxidant/antioxidant imbalance may be connected to the complex mechanism leading to the DNA damage indicated in the blood of patients with head and neck cancer.

Mitochondrial DNA polymorphism in genes encoding ND1, COI and CYTB in canine malignant cancers

The aim of the study was to identify DNA changes in mitochondrial gene fragments: NADH dehydrogenase subunit 1 (ND1), cytochrome c oxidase subunit I (COI) and cytochrome b (CYTB) in tumor tissue, normal tissue and blood, and to define their association with the tumor type in dogs. Molecular analysis included 144 tests in total. A functional effect of the non-synonymous protein coding SNP was predicted. The presence of polymorphisms in all tested gene fragments in individual tissues of dogs was observed. Heteroplasmic changes were found in ND1 and CYTB in epithelioma glandulae sebacei and in CYTB in lymphoma centroblasticum. The results of in silico analysis show the impact of these alleles (COI: 507, ND1: 450, 216, CYTB: 748) on the functioning of proteins and thus their potential role in carcinogenesis. The possible harmful effects of changes in polypeptides in positions T193N, V98M, V118M and H196P were evaluated. It seems that polymorphisms occurring in cells can have a negative impact on functioning of proteins. This promotes disorders of the energy level in cells.

The role of the mitochondrial genome in ageing and carcinogenesis

Mitochondrial DNA mutations and polymorphisms have been the focus of intensive investigations for well over a decade in an attempt to understand how they affect fundamental processes such as cancer and aging. Initial interest in mutations occurring in mitochondrial DNA of cancer cells diminished when most were found to be the same mutations which occurred during the evolution of human mitochondrial haplogroups. However, increasingly correlations are being found between various mitochondrial haplogroups and susceptibility to cancer or diseases in some cases and successful aging in others.

Molecular oncology focus - is carcinogenesis a 'mitochondriopathy'?

Mitochondria are sub-cellular organelles that produce adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS). As suggested over 70 years ago by Otto Warburg and recently confirmed with molecular techniques, alterations in respiratory activity and in mitochondrial DNA (mtDNA) appear to be common features of malignant cells. Somatic mtDNA mutations have been reported in many types of cancer cells, and some reports document the prevalence of inherited mitochondrial DNA polymorphisms in cancer patients. Nevertheless, a careful reanalysis of methodological criteria and methodology applied in those reports has shown that numerous papers can't be used as relevant sources of data for systematic review, meta-analysis, or finally for establishment of clinically applicable markers. In this review technical and conceptual errors commonly occurring in the literature are summarized. In the first place we discuss, why many of the published papers cannot be used as a valid and clinically useful sources of evidence in the biomedical and healthcare contexts. The reasons for introduction of noise in data and in consequence - bias for the interpretation of the role of mitochondrial DNA in the complex process of tumorigenesis are listed. In the second part of the text practical aspects of mtDNA research and requirements necessary to fulfill in order to use mtDNA analysis in clinics are shown. Stringent methodological criteria of a case-controlled experiment in molecular medicine are indicated. In the third part we suggest, what lessons can be learned for the future and propose guidelines for mtDNA analysis in oncology. Finally we conclude that, although several conceptual and methodological difficulties hinder the research on mitochondrial patho-physiology in cancer cells, this area of molecular medicine should be considered of high importance for future clinical practice.

[Metabolic markers of the head and neck cancers--clinical applications and the biochemical background]

The problem of diagnosis in the field of head and neck region is still valid. Specific diagnosis and precise estimation of the tumor's size with the use of CT and MRI imaging is generally unsatisfactory. The Positron Emission Tomography (PET) supports this process with additional information about the tumor's metabolism. Numerous publications show that PET-CT has a great influence on the evaluation of the size of the tumor, presence of lymph node metastases, choice of treatment and the prognosis of the recurrence. Cancer cells represent a specific metabolic state. These cells intake large quantities of glucose and utilize it in the process of glycolysis. The oxidative phosphorylation is not efficient in the transformed cells and defects in mitochondrial functions are at the heart of malignant cell transformation. Disruption of the oxidative phosphorylation chain has been described in the neoplasms. As a consequence, in cancer the glycolysis is active even in the normoxic environment. This metabolic shift in cell transformation has been described in early XX century and so called Warburg's hypothesis profoundly influenced the present perception of cancer metabolism, positioning what is termed aerobic glycolysis in the mainstream of clinical oncology. Today we know that neoplastic cells differ at the proteomic level. A subset of different proteins such as hexokinase II or HIF are upregulated. These abnormalities might be used as the neoplastic markers.

Common mitochondrial polymorphisms as risk factor for endometrial cancer

Endometrial carcinoma is the most commonly diagnosed gynaecological cancer in developed countries. Although the molecular genetics of this disease has been in the focus of many research laboratories for the last 20 years, relevant prognostic and diagnostic markers are still missing. At the same time mitochondrial DNA mutations have been reported in many types of cancer during the last two decades. It is therefore very likely that the mitochondrial genotype is one of the cancer susceptibility factors. To investigate the presence of mtDNA somatic mutations and distribution of inherited polymorphisms in endometrial adenocarcinoma patients we analyzed the D-loop sequence of cancer samples and their corresponding normal tissues and moreover performed mitochondrial haplogroup analysis. We detected 2 somatic mutation and increased incidence of mtDNA polymorphisms, in particular 16223C (80% patients, p = 0.005), 16126C (23%, p = 0.025) and 207A (19%, p = 0.027). Subsequent statistical analysis revealed that endometrial carcinoma population haplogroup distribution differs from the Polish population and that haplogroup H (with its defining polymorphism - C7028T) is strongly underrepresented (p = 0.003), therefore might be a cancer-protective factor. Our report supports the notion that mtDNA polymorphisms establish a specific genetic background for endometrial adenocarcinoma development and that mtDNA analysis may result in the development of new molecular tool for cancer detection.